<B> is the keycombo for interfacing with tmux. Once you have hit this key combo, you may let go, and then proceed to issue further key
sequences(not push and hold, just tapped in sequence).
Once you have hit
PgUp to scroll the pane upwards, and
PgDown for downwards. Use the arrow keys to move focus from one pane to the next,
% to split vertically and
" to split horizontally. just type
exit to close a pane or use
x. If you have issues with copying text when you have multiple panes open, you can fullscreen the current pane using
z, which will negate the issue of copying text from multiple panes.
If you require to copy more than a shells height worth of text, you probably want to use the OS buffer instead. Hit
v to enter visual mode, and
j to select from the current position, until the next line. Repeat
j until all desired text is selected, and finally type
"*y which will yank to the OS buffer, you may then use
"*p to paste: Copy and paste
Hope this helps!